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Page 78 of 378
ITG Engineering Guidelines
Table 5
Silence suppression enabled, T-LAN Ethernet and WAN IP bandwidth usage per ITG port
(Part 2 of 2)
Codec
Multi -
frame
Codec type
duration
in ms
(payload)
(one way)
30
G.723.1
(5.3
kbit/s)
G723.1
30
(6.3
kbit/s)
T.30/T38
G3 Fax
16.6
Modem
25
(14.4
kbit/s)
Note 1: Based on voice multiframe encapsulation for Realtime Transport Protocol per H.323 V2.
Note 2: The bolded rows contain the default payload/packet size for each codec in the MAT.
Note 3: T-LAN data rate is the effective Ethernet bandwidth consumption.
Note 4: 40% voice traffic reduction due to silence suppression; no suppression for fax.
Note 5: T-LAN kbit/s for voice traffic = (1-40%)*2*Ethernet frame bits*8/frame duration in ms
Note 6: WAN kbit/s for voice traffic = (1-40%)*IP packet bytes*8/frame duration in ms
Note 7: 24 ports per card for all codecs
Note 8: Overhead (RTP/UDP header + IP header) of packets over the voice payload multiframe is 40
bytes; overhead of Ethernet frame over IP packet is 26 bytes.
Note 9: The above bandwidth calculation does not include an Interframe gap, because of the low
probability of occurring in this type of application.
Disable silence suppression at tandem nodes
553-3001-202
Standard 1.00
Voice/fax
payload
IP voice
Multi -
packet in
frame
bytes
in bytes
(one way)
(one way)
20
60
24
64
30
70
30
70
Silence suppression introduces a different concept of half-duplex or
full-duplex at the voice message layer that results in a kind of statistical
multiplexing of voice messages over the WAN.
When Meridian 1 equipped with an ITG node serves as a tandem switch in a
network where some circuit-switched trunk facilities have an excessively low
audio level, silence suppression, if enabled, will degrade the quality of service
by causing choppiness of speech. Under tandem switching conditions with
April 2000
Ethernet
Bandwidth
voice
use on
packet in
T-LAN in
bytes
kbit/s
(one way)
(two way)
86
27.5
90
28.8
96
46.1
96
30.7
WAN with
Bandwidth
Frame
use on
Relay
WAN in
overhead
kbit/s
in kbit/s
(one way)
(one-way)
9.6
10.9
10.2
11.5
33.6
37.5
22.4
25.0
WAN with
ATM
overhead
in kbit/s
(one-way)
17.0
17.0
50.9
33.9
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